The present invention relates to methods and apparatus for monitoring the operation of sucker-rod well pumping units, and more particularly to methods and apparatus for recording and subsequent playback of selected dynagraphs for wells employing sucker-rod pumping units.
Sucker-rod type pumping units are widely used in the petroleum industry in order to recover fluid from wells extending into subterranean formations. Such units include a sucker-rod string which extends into the well and means at the surface for an up and down movement of the rod string in order to operate the plunger of a downhole pump. Typical of such units are the so called "beamtype" pumping units having the sucker-rod string suspended at the surface of the well from a structure consisting of a Samson post and a walking beam pivotally mounted on the Samson post. The sucker-rod string normally is connected at one end of the walking beam and the other end of the walking beam is connected to a prime mover such as a motor through a suitable crank and pitman connection. In this arrangement the walking beam and the sucker-rod string are driven in a reciprocal mode by the prime mover.
When a problem causes a well to be shut down it is desirable to review the operating conditions immediately prior to well shutdown. This may be done by observing the historical dynagraphs of an instrumented, controlled rod pumped well including:
(1) The dynagraphs utilized by the instrument to calibrate itself.
(2) The dynagraphs just prior to shutdown of the well by the well controller or by other means.
To make this possible, the well controller must save in its memory, a series of load-stroke data points for subsequent playback on an X-Y plotter or other similar device, upon request at sometime in the future. The amount of information which is saved is limited by the amount of memory space available, so it is desirable to compress the data prior to storage in order to conserve memory space.
It is further desirable to display these dynagraphs relative to some absolute frame of reference such as a minimum load limit and a maximum load limit. It is also beneficial to include the thresholds and/or setpoints that the controller detector(s) were using at the time the dynagraphs were recorded.